The present invention relates to a catalyst composition suitable for hydrocarbon conversion processes such as isomerization, alkylation and polymerization. More particularly, the present invention relates to a catalyst composition comprising hydrogen fluoride-antimony pentafluoride on an alumina support, and the use of the catalyst in processes such as isomerization.
Isomerization of normal paraffins such as n-pentane, n-hexane or n-heptane is widely practiced for production of higher-octane isomers for use in gasoline.
Table I, below, shows the incentive for isomerization.
TABLE I ______________________________________ Research Octane Motor Octane 3 cc. 3 cc. Hydrocarbon Clear TEL Clear TEL ______________________________________ n-Pentane 62 89 62 84 i-Pentane 92 109 90 105 n-Hexane 25 65 26 65 2-methylpentane 73 93 74 91 3-methylpentane 75 93 74 91 2,2-Dimethylbutane 92 106 93 113 (neohexane) 2,3-Dimethylbutane 103 119 94 112 (diisopropyl) ______________________________________
Isomerization processes can be divided into high, low, and ultra-low temperature processes. Rough temperature ranges are: 500.degree.-800.degree.F. for high-temperature isomerization; 150.degree.-400.degree.F. for low-temperature isomerization; and -50.degree.F. to 150.degree.F. for ultra-low-temperature isomerization. In the past, commercial operation has been mostly low-temperature isomerization utilizing a catalyst containing AlCl.sub.3.
For typical low-temperature isomerization, the catalyst used is AlCl.sub.3 plus hydrogen chloride. Low-temperature isomerization feedstock, dried and preheated to reaction temperature, is combined with a recycle stream (if recycling is practiced), mixed with hydrogen chloride, and passed through a reactor and an aluminum chloride recovery section. Reactor effluent is cooled and flashed to discharge any light gases through a small absorber that recovers hydrogen chloride carried off in the gases. Liquid from the flash drum is stripped to recover hydrogen chloride, and is caustic-washed to remove the last traces of acid. The stripping column is usually operated at a pressure high enough that the stripped hydrogen chloride can be returned directly to the reactor. If recycling of unconverted normal paraffin is practiced, the recycle stream is then fractionated from the product.
______________________________________ Typical reaction conditions are: Catalyst AlCl.sub.3 --HCl Inhibitor H.sub.2 (60 psi) Pressure, psi 300 Temperature, .degree.F. 176 - 212 Space Velocity, V/hr/V 1.0 - 2.5 HCl Conc., Wt.% 5 Conversion % 60 ______________________________________
Ultra-low temperature isomerization so far has not been commercially employed. However, there is considerable incentive to develop a commercially attractive low-temperature isomerization process, because the lower the temperature the more favorable is the equilibrium for isoparaffin relative to normal paraffins. Ultra-low temperatures are especially attractive for substantial production of the very high-octane dimethylbutanes.
U.S. Pat. No. 2,956,095 describes an ultra-low-temperature isomerization process employing a fluorosulfonic-acid catalyst instead of a Friedel-Crafts type catalyst such as AlCl.sub.3.
U.S. Pat. No. 3,201,494 and U.S. Pat. No. 3,394,202 are also directed to ultra-low-temperature isomerization and are especially pertinent to the present invention.
U.S. Pat. No. 3,201,494 is directed to liquid-phase isomerization of hydrocarbons using a hexafluoro-antimonic acid catalyst in hydrofluoric acid, which catalyst is obtained, according to Example 1 of the patent, by dissolving antimony pentafluoride in hydrofluoric acid.
U.S. Pat. No. 3,394,202 is also directed to isomerization using a hydrogen fluoride-antimony pentafluoride acid catalyst, but is the U.S. Pat. No. 3,394,202 the catalyst is supported on an inert support such as fluorided alumina. According to U.S. Pat. No. 3,394,202:
"...suitable inert carriers may be prepared from solids which are not inert but which have been treated to make them inert, e.g., coated with a thin layer of inert material. This embodiment of the invention may be preferred in many cases, since it is usually desirable to support the acid on a carrier having a high surface area for maximum contact area with hydrocarbons to be converted. ...An example of material having a high surface area which may be treated to provide supports of the invention are alumina, silica, ... Although the specific surface area of the porous carrier is slightly decreased as a result of the treatment, inert carriers with a specific surface area of at least 100 m.sup.2 /gm. are easily prepared. Desirable surface areas are from 10 to about 500 m.sup.2 /gm., preferably 20 to 200 m.sup.2 /gm., with pore diameters greater than 10 A, and preferably 100-1000 A." PA1 " ...a surface area of about 50 square meters per gram to about 1000 square meters per gram or more, and which, when combined with the active catalytic complex will not substantially lower the catalytic activity of the combined complex, nor will the complex destroy the structural integrity and surface area of the solid support."
Quite similar to U.S. Pat. No. 3,394,202, U.S. Pat. No. 3,678,120 is directed to a catalyst composition comprising HF-antimony pentafluoride on an inert support, such as charcoal. According to U.S. Pat. No. 3,678,120, the inert support should have:
My U.S. Pat. No. 3,852,371 discloses an alkylation process using a fluorided alumina catalyst, in which a portion of the effluent from the reaction zone is recycled thereto.